The JMC 7 Downloads available from
Unlike the JMC 7 EA builds, which included the JDK, they seem to expect the JDK in a particular location and when its not found they fail.
Tried this on macOS 10.14 (mac OS version) and on Windows 10 (Windows version).
The Windows error message refers to a directory that doesn't exist:
C:\Users\aurelio\Downloads\jmc-7+14_windows-x64_bin\jmc-7+14_windows-x64\bin does not contain a jre directory